The earning power of young single women has surpassed that of their male peers in metropolitan areas around the U.S., a shift that is being driven by the growing ranks of women who attend college and move on to high-earning jobs. In 2008, single, childless women between ages 22 and 30 were earning more than their male counterparts in most U.S. cities, with incomes that were 8% greater on average, according to an analysis of Census Bureau data released Wednesday by Reach Advisors, a consumer-research firm in Slingerlands, N.Y.